newly added instance methods in the derived class of JSClassref is not getting called

Created a new JSClassref using JSClassDefinition in JavascriptCore and when creating a derived class in javascript files and adding additional functions, the additional functions are not getting called with newly created derived class instance object.
In the below code when loaded in JSContext
class student1 {

   constructor(firstName, lastName) {
     this.firstName = firstName;
     this.lastName = lastName;
   }

   intro() {
     return Hello i am ${this.firstName} ${this.lastName};
   }
}
class Studentdetails1 extends student1 {

   constructor(firstName, lastName, phone, address) {
     super(firstName, lastName);
     this.phone = phone;
     this.address = address;
   }
   studentName(){
    return this.firstName;
  }
}
var Studentdetails1Object = new Studentdetails1("ios","iphone","999999999","hyderabad-india");
Studentdetails1Object.studentName() // WORKS PROPERLY


// BNRContact is new js object added using javascriptcore
class childBNRContact extends BNRContact{
  constructor(){
    super()
  }
  helloFunc(){
    return "hello World!";
  }
}
var childBnrObject = new childBNRContact();
childBnrObject.helloFunc() // NOT WORKING